import 'dart:async';

Timer? tt;
void main(){
  // testTimer();
  print("hello");

  tt = Timer.periodic(Duration(seconds: 1), (Timer t){
    // t.cancel();
    print("aaa${tt == t}");
  });
}

void testTimer(){
  Timer? timer;
  timer = Timer(Duration(seconds: 3), (){
    print("callback");
  });
  // timer.cancel();

  print("world");
}